Smoothbore barrel wall thickness

[gumboman]

Planning next gun build project. Will be an English style flintlock fowling piece in 12 gauge.

Will have the barrel jug choked.

Barrel will be octagon to round, with round section tapered and flared.

I need to tell the barrel maker what the minimum wall thickness of the barrel should be at the waist.

Can anyone with experience provide some input and guidance on this?

Total choke will be .025" (.0125" per side) to provide a full choke. I am thinking a wall thickness at the smallest diameter should be .100" which will leave a thickness at the choke of .0875 after work is done

The person who will do the jug choke recommends a wall thickness before choking of .90" which will leave a wall thickness of .0775" at the choke.  I will feel safer with a.100" before choking but do not want to end up with a muzzle heavy gun.

Would appreciate words of advice from those who have been there and have experience with this.

[jerrywh]

 What type of steel is it made of? Modern shotgun of 12 ga. usually only have about .050 or less. A black powder shotgun of 12ga. only produces about 3000psi at the chamber with a standard load. Shot only.

[gumboman]

Steel will be 12L14.

[jerrywh]

 I have seen a lot of Belgian made shotguns that shoot black powder on some of them the barrels are only .035 thick 12" from the muzzle. I tested a set of barrels 28ga. On those barrels the barrel was only .032 About 9" from the breech. They withstood 150grs. of ffg and one .54 patched rb three times. The metal was 1137 barrel steel from a prominent barrel maker.
  Read this article.   https://books.google.com/books?id=Dzxyneq43AEC&pg=PA105&lpg=PA105&dq=black+powder+shotgun+pressure&source=bl&ots=6jh0NhGmqT&sig=RKsrw3J4Ol-hqzvZkeD68dw-1c0&hl=en&sa=X&ved=0CCYQ6AEwAWoVChMIy7qFudCIxgIVCX2ICh1xAQD5#v=onepage&q=black%20powder%20shotgun%20pressure&f=false
By the time the shot column reaches a point 24" down the bore the pressure drops dramatically and is almost insignificant unless the bore is obstructed. These things  only apply to shotguns loaded properly.   

[Bob Roller]

Green Mountain barrels have been made from 1137M for a long time. The "M"stands for modified according to a steel company I raised an inquiry with. The fellow I talked with said 1137 could be modified for gun barrels and truck axles and a variety of other uses but I think he said the minimum order was 20 tons.'
12L14 makes great screws as was its intended use.

Bob Roller

[JCKelly]

Bob, you should know that I have the greatest respect for your work.
So I feel hesitant to criticize your remark on 12L14 -

But I think 12L14 makes a lousey screw. If the thing rusts a bit, binds up, it will shear off like Extra Sharp Cheddar when you try to unscrew it.

I take care to keep your locks clean & oiled.

12L14 was developed for automatic screw (a.k.a. "love") machines to reliably turn out large numbers of parts quickly. Most hardware store screws are 12L14.

What does this have to do with a gun barrel question, anyway?

[Bob Roller]

Steel will be 12L14.

This is what raised the issue.

Bob Roller

[little joe]

Ask your barrel maker and take there suggestions as to what is safe and go from there.

[bob in the woods]

I would suggest not getting concerned about telling barrel makers how to make their barrels.  I've used many Getz, Long Hammock and Colerain smoothbore barrels and never had any issues.  I figure they know what they're doing.

[SuperCracker]

FWIW.  This diagram is from the earlyish breech loading era.


That said.  I would recommend telling the barrel maker what you're planning on doing with it, what kind of gun you're planning on building and a general idea of what you're looking for and then let him make what's appropriate and safe.

[WadePatton]

FWIW.  This diagram is from the earlyish breech loading era.


That said.  I would recommend telling the barrel maker what you're planning on doing with it, what kind of gun you're planning on building and a general idea of what you're looking for and then let him make what's appropriate and safe.

Better advice cannot be given.

[jerrywh]

In the [complete black powder handbook] you can find where Goex performed pressure tests on shotgun barrels. Many early black powder guns and some made for smokeless powder were made from what they called decarbonized steel.  I have worked on some of these barrels and they are as soft as butter.  I was looking at a set of 410 Belgian barrels last night. They are only about .035 at the muzzle and are twist steel. A 410 ga. generates a lot more pressure than a 12 ga. does.  I had a few discussions about this with John Getz and we agreed that most people today have a fear of barrel failure that is unjustified.  12L14 makes great screws when case hardened and they should be. Otherwise they are way too soft. 12L14 also makes great muzzle loading barrels. There has to be at least 1/2 a million of them out there. So far nobody has ever been able to show me one that has blown up. I wouldn't want to try it but I haven't even heard of one failing from being short started.   Many times I have asked for proof of a Getz barrel failure . Can someone show me one with proof.   I saw a 4140 barrel blow up from being double loaded with black powder  super imposed loads once. The guys handle is now BAD  HAND.

[bob in the woods]

Don Getz  [ my, how I miss his contributions    ]    once told a story about taking a 10 or 12 inch section of barrel, filling it with powder and breaching both ends. There was a touch hole drilled in the middle of the barrel with a fuse inserted.  They lit the fuse, the thing "went off " and the barrel held     I believe the comment was that he couldn't imagine all that fire coming out the touch hole…but it did ! "    I've seen one barrel  , a 1 in oct.  .54  , bulge due to a short started ball , and I've seen one other barrel with a small split due to a short started ball and a dovetail cut deep for a barrel lug.

[jerrywh]

 When I talked to John about 12 years ago I found out that they did the same test as I did on the plugged barrel. My intent was to make a big firecracker if you will. On my experiment all the pressure came out the touch hole just as his did. However I sure wouldn't want to standing around there and do it again. I was only about 18 years old when I did that. I think the touch hole was 1/8"

[MikeEasy]

What type of steel is it made of? Modern shotgun of 12 ga. usually only have about .050 or less. A black powder shotgun of 12ga. only produces about 3000psi at the chamber with a standard load. Shot only.

I think the 3000 psi estimate is low. For example, at http://www.shotgunworld.com/bbs/viewtopic.php?t=259371 they speak of black powder shotgun pressures from 6000 psi - 20,000 psi. 

Safety First!

[greybeard]

Over the years I owned many fine english sporting doubles by Westley Richards, Manton, Harkom to name a few and nary a one had enough at the muzzle to jug choke. Wall thikness at the muzzle were 30 - 35 thou on most of them. Not a lot of pressure at the muzzle.
Bob

[jerrywh]

What type of steel is it made of? Modern shotgun of 12 ga. usually only have about .050 or less. A black powder shotgun of 12ga. only produces about 3000psi at the chamber with a standard load. Shot only.

I think the 3000 psi estimate is low. For example, at http://www.shotgunworld.com/bbs/viewtopic.php?t=259371 they speak of black powder shotgun pressures from 6000 psi - 20,000 psi.  

Safety First!

   The tests in the book I refered to were done by Lyman and the powder was ffg Goex and Sam Fadala is probably the most respected black powder load expert in the USA.  

[bob in the woods]

I had an old shotgun with a hole drilled through the barrel near the muzzle , which had a brass bead "press fit " by a previous owner [ a relative ]  Not threaded…the threads were stripped. That bead never blew out, and yet a good bump knocked it off one day .   

[Ryan McNabb]

I've never seen a modern trade gun barrel that was as thin and delicate as an 18th century original, nor have I been able to have one made no matter how I ask.  To me this is one of the great unobtainable things in this trade. (Two others are a reliable source of hand forged hardware and set triggers that look like originals, but I digress.)

[Mike Brooks]

I've never seen a modern trade gun barrel that was as thin and delicate as an 18th century original, nor have I been able to have one made no matter how I ask.  To me this is one of the great unobtainable things in this trade. (Two others are a reliable source of hand forged hardware and set triggers that look like originals, but I digress.)

My Carolina barrels are as thin as the originals. Hoyt makes those for me. Copied directly from an original 18th century Carolina gun.

[Ryan McNabb]

Mike thanks...that's great.  I've never heard of him before, but I found he works at the Freischutz shop.  Thanks again.

[gumboman]

Can anyone with past experience comment on minimum barrel thickness for a smooth bore on a newly made barrel that will get a jug choke?

The guys at Colerain have said their 12 bore has a diameter of .850 at the waist that gives .046 wall thickness which does not leave enough.

[Dennis Glazener]

But your jug choke does not go in the waist. Colerain should be able to tell you since thry sell jug choked barrels. I don't think you remove  but a few thousandth's for the "jug".
Dennis

[jerrywh]

 About .020" is a full choke, maybe .025" That is only 10 or 12 to the side.

[gumboman]

For those interested, this is what I have uncovered so far in my search for a 12 gauge smooth bore with jug choke.

The person referred to me that can actually machine the barrel for the jug choke told me for a full choke he would remove .0125" per side. The choke would start approximately 1 inch from the muzzle and extend back toward the breech for 5-6 inches. This length would reach into the waist area of a Colerain barrel. Colerain does not recommend this procedure on their barrels as the waist area is too thin.

Colerain does not perform jug choke services. They do offer the turkey choke in a 20 gauge and the choke is accomplished by restricting the .620" bore down to .580 at the muzzle.

The person who can perform the jug choke machining recommended a .090" minimum wall thickness before the full choke machining is performed. This would leave .077" wall thickness after machining.  My instinct tells me the minimum should be higher but I don't have actual experience in this matter.

At the end of the day I will likely go with the .090" minimum.